1. Field of the Invention
The present invention generally relates to a bond pad structure and, more particularly, to a bond pad structure with a protection layer.
2. Description of the Prior Art
In semiconductor manufacturing, a fabricated integrated circuit (IC) device is typically assembled into a package to be utilized on a printed circuit board (such as a motherboard, etc) as part of a larger circuit. When the fabrication of the integrated circuit device (such as a die) is finished, the integrated circuit device is immovably bound and sealed using an electronic package technique so as to prevent damages from an external force or other environmental factors. A package substrate is often used in the electronic package industry to affix the integrated circuit device thereon, and it also provides one or more layers of metal interconnects, wherein one end of the metal interconnect is electrically connected to the integrated circuit device, and the other end thereof is electrically connected to the other electronic modules. The metal bond pad (or referred to as bonding pad) is designed to be in the openings of the passivation layer (i.e. topmost insulating layer) of the integrated circuit device as a mean to connect the metal interconnects of the package substrate to the integrated circuit device.
In the past, aluminum or aluminum alloys, such as AlCu alloy or AlSiCu alloy, have been used as conventional chip wiring materials. More recently, aluminum wiring material has been replaced by copper and copper alloys with damascene process, since copper wiring can provides improved chip performances and superior reliability when compared to aluminum and aluminum alloys. However, in the packaging of IC devices, employing copper wiring may induce a number of process issues, such as the reaction of copper with the material used in the ball-soldering process, and/or the susceptibility of copper to the environmental damages and corrosion. To solve these process issues, a terminal aluminum pad or aluminum cap structure is designed to be formed on the copper interconnection for protecting the copper from environmental deterioration.
Although the use of an aluminum pad/cap structure on the copper interconnection may solve the conventional copper deterioration issues, it still has some process drawbacks to improve. As well-known in the semiconductor field, aluminum materials are quite vulnerable to the corrosion issue, especially for the aluminum structure in the aforementioned pad loop. In this process stage, a thick photoresist layer used for patterning the aluminum pad may leave residues on the surface of aluminum layer due to the PR hardening, thereby significantly increasing the possibility of Al corrosion. This is major cause of the so-called “pad discoloration” issue.
Therefore, while aforementioned existing methods of fabricating bond pad structures for semiconductor devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in every aspect. There is still a need to improve the bond pad structure and the manufacturing method thereof in order to provide larger process windows as well as to lower the process costs.